Very low temperature refrigeration system having a scroll compressor with liquid injection

Abstract

Disclosed is a very low temperature or cryogenic refrigeration system with a scroll compressor and utilizing a mixed refrigerant that decreases refrigerant discharge temperature by refrigerant injection into the compressor.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application is a continuation application of International Application PCT / US2003 / 029211 filed Sep. 18, 2003, now International Publication WO 2004 / 027324 and claims the benefit of U.S. Provisional application No. 60 / 411,676 filed Sep. 18, 2002, the contents of which are herein wholly incorporated by reference.BACKGROUND OF THE INVENTION[0002]Refrigeration systems have been in existence since the early 1900s, when reliable sealed refrigeration systems were developed. Since that time, improvements in refrigeration technology have proven their utility in both residential and industrial settings. In particular, very low temperature refrigeration systems currently provide essential industrial functions in biomedical applications, cryoelectronics, optical coating operations, industrial and commercial coating operations, and semiconductor manufacturing applications. Refrigeration systems manufacturers are also faced with increasingly restri...

AI Technical Summary

Benefits of technology

[0032]The present invention represents an increased efficiency modification of prior art systems, providing improved efficiency. A significant difference between the presently disclosed systems and the prior art is that the present systems use a scroll compressor with liquid injection for cooling in a very low temperature refrigeration system with a mixed refrigerant having a high content of low boiling point refrigerants. The low boiling point refrigerant can comprise from about fifteen percent to over fifty percent of the refrigerant mixture, preferably less than fifty percent and most preferably in the range of from about 20 to about 45% of the refrigerant mixture.

[0036]The addition of refrigerant to the compression process after the two scrolls have enclosed a gas pocket at suction pressure enables a higher refrigerant mass flow rate. Increasing the mass flow rate results in greater refrigeration efficiency.

[0037]Managing the presence of warm boiling liquid refrigerants such that they do not adversely separate from the mixture and accumulate in the compressor sump allows higher concentrations of these refrigerants than could be supported with scroll compressors without liquid injection. This improves overall refrigeration efficiency through several means such as increased heat rejection, and / or the ability to use higher concentrations of low boiling components, or the ability to operate over higher compression ratios.

[0038]The disclosed systems include a highly efficient, high capacity, compact scroll compressor that manages the discharge temperature of the mixed refrigerant containing low boiling refrigerants. An advantage of the disclosed system is that the circulation of warm boiling refrigerant components is managed such that excess amounts do not accumulate in the compressor oil sump while the compressor is operating. This improved management results in lower compressor discharge temperatures and makes possible improved overall system efficiency.

[0064]The oil sump heater or crankcase heater is a standard component on refrigeration systems and serves the purpose of preventing refrigerant from flooding the compressor during startup. In this application, it is intended that the crankcase heater be optional. However, if used, it can be used in two ways. The first method is to energize this heater only when the compressor is off for the purpose of minimizing refrigerant liquids in the compressor sump. However, on mixed refrigerant systems for very low application, this is typically not very effective since the typical temperatures achieved by these heaters do not effectively reduce such liquid refrigerants due to their very low vapor pressures and corresponding warm normal boiling points.

[0066]In a preferred embodiment, the present system is an very low temperature refrigeration system that uses a scroll compressor having liquid injection for lowering the discharge temperature and an optional heater for oil sump warming that improves the overall system efficiency compared to scroll compressors without liquid injection while minimizing the size of the system as compared with refrigeration systems using conventional reciprocating compressors.

Problems solved by technology

Refrigeration systems manufacturers are also faced with increasingly restrictive environmental regulations that have driven the refrigeration industry away from chlorinated fluorocarbons (CFCs) to hydrochlorinated fluorocarbons (HCFCs), and more recently, to hydrofluorocarbons (HFCs) due to a European Union law (in effect January 2001) banning use of HCFCs.

Semi-hermetic reciprocating compressors are particularly large, adding to the required floor space of a refrigeration system.

Steady state operation will typically be limited temperatures lower than 130° C. Temperatures in excess of 130° C. result in decomposition of the compressor oil and subsequent metal wear which results in a compressor failure.

In a typical unit, the discharge temperature of a scroll compressor imposes a significant limitation on the operating conditions of the compressor and reduces overall system efficiency.

Unfortunately, this system does not have a desirably high efficiency.

Unfortunately, this system does not have a desirably high efficiency.

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